Mycoflora dynamics analysis of Korean traditional wheat-based nuruk

Abstract

The growing popularity of traditional Korean alcoholic beverages has led to a demand for quality enhancement of the traditional starter culture nuruk, which consists primarily of wheat. Therefore, this study focused on mycoflora characterization and the temporal variations in traditional wheat-based nuruks fermented at two representative traditional temperature conditions for 30 days. Nuruk A was fermented at a constant temperature of 36°C for 30 days and nuruk B was fermented at a high initial temperature of 45°C for 10 days followed by 35°C for 20 days. The average mycoflora load in the two different nuruk conditions did not vary significantly between the 0 and 30 day cultures, and a maximum load of 8.39 log CFU/g was observed for nuruk A on culture day 3 and 7.87 log CFU/g for nuruk B on culture day 30. Within two samples, pH was negatively correlated with temporal changes in mycoflora load. The pH of nuruk A was significantly lower than that of nuruk B at all of the time points evaluated. Culture-dependent characterization led to the identification of 55 fungal isolates belonging to 9 genera and 15 species, with the most prominent genera comprising Lichtheimia, Penicillium, Trametes, Aspergillus, Rhizomucor, and Mucor. A total of 25 yeast isolates were characterized belonging to 6 genera and 7 species, the most prominent among which were Rhodotorula, Pichia, Debaryomyces, Saccharomycopsis, and Torulospora. Mycofloral community dynamics analysis revealed that both samples A and B varied considerably with respect to the fungal communities over a span of 30 days.

Taxonomic Characterization, Evaluation of Toxigenicity, and Saccharification Capability of Aspergillus Section Flavi Isolates from Korean Traditional Wheat-Based Fermentation Starter Nuruk

“…Recent global demands for Korean alcoholic beverages have elicited the need for more efficient and safer starter cultures. Aspergilli strains have been frequently isolated from Korean starter cultures nuruk [13202122]. In this study, we isolated Aspergillus strains from traditional wheat-based nuruk fermented under different fermentation conditions, including varying temperature and moisture and evaluated their toxigenicity and efficiency.…”

“…In this study, we isolated Aspergillus strains from traditional wheat-based nuruk fermented under different fermentation conditions, including varying temperature and moisture and evaluated their toxigenicity and efficiency. As DRBC is the best medium to support controlled growth of fungi and yeasts without bacterial contamination [13], we applied serially diluted suspensions of traditional wheat-based nuruk from our previous study [13] to DRBC plates and a total of 69 presumed Aspergillus species with floccose and grayish yellow to olive colonies were isolated. Further taxonomical identifications were carried out on a molecular basis involving the ITS and CF gene sequences.…”

“…For molecular characterization, DNA was extracted from all of the isolates according to the protocol described by Bal et al [13]. The ITS region of the rRNA gene and partial CF gene were sequenced from each isolate for molecular identification.…”

Concept of Nuruk on Brewing Technology

“…Currently, research on the production of certain traditional Nuruk [2][3][4], Nuruk-derived microorganisms [5][6][7][8][9], traditional Nuruk-derived Korean alcoholic beverages [10][11][12][13], and their physiological functions [14][15][16][17] are being performed. In addition, investigation on the Nuruk microbial communities [18][19][20] as well as the metabolite analysis of Nuruk [20] was recently performed.…”

Whole-genome de novo sequencing, combined with RNA-Seq analysis, reveals unique genome and physiological features of the amylolytic yeast Saccharomycopsis fibuligera and its interspecies hybrid

“…This yeast has been considered one of the best producers of amylolytic enzymes among ascomycetous yeast species [3], since its capacity to perform starch hydrolysis was first reported by Wickerham et al [4]. It is commonly found as a dominant yeast species in traditional Asian alcoholic starters for rice wine production, such as ‘ Daqu ’ in China [5], ‘ Ragi ’ in Indonesia [6], ‘ Loogpang ’ in Thailand [7], ‘ Banh Men ’ in Vietnam [8], and ‘ Nuruk ’ in Korea [9]. In addition, S. fibuligera was cultivated alone on starchy waste in Czechoslovakia or in mixed culture with Candida utilis on potato-processing wastes in Sweden to produce single-cell protein, which was used for protein supplementation in animal feeds [10].…”